lkml.org 
[lkml]   [2020]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH 4.4 119/135] blktrace: break out of blktrace setup on concurrent calls
    Date
    From: Luis Chamberlain <mcgrof@kernel.org>

    [ Upstream commit 1b0b283648163dae2a214ca28ed5a99f62a77319 ]

    We use one blktrace per request_queue, that means one per the entire
    disk. So we cannot run one blktrace on say /dev/vda and then /dev/vda1,
    or just two calls on /dev/vda.

    We check for concurrent setup only at the very end of the blktrace setup though.

    If we try to run two concurrent blktraces on the same block device the
    second one will fail, and the first one seems to go on. However when
    one tries to kill the first one one will see things like this:

    The kernel will show these:

    ```
    debugfs: File 'dropped' in directory 'nvme1n1' already present!
    debugfs: File 'msg' in directory 'nvme1n1' already present!
    debugfs: File 'trace0' in directory 'nvme1n1' already present!
    ``

    And userspace just sees this error message for the second call:

    ```
    blktrace /dev/nvme1n1
    BLKTRACESETUP(2) /dev/nvme1n1 failed: 5/Input/output error
    ```

    The first userspace process #1 will also claim that the files
    were taken underneath their nose as well. The files are taken
    away form the first process given that when the second blktrace
    fails, it will follow up with a BLKTRACESTOP and BLKTRACETEARDOWN.
    This means that even if go-happy process #1 is waiting for blktrace
    data, we *have* been asked to take teardown the blktrace.

    This can easily be reproduced with break-blktrace [0] run_0005.sh test.

    Just break out early if we know we're already going to fail, this will
    prevent trying to create the files all over again, which we know still
    exist.

    [0] https://github.com/mcgrof/break-blktrace

    Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
    Signed-off-by: Jan Kara <jack@suse.cz>
    Reviewed-by: Bart Van Assche <bvanassche@acm.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/trace/blktrace.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
    index 6737564680193..8ac3663e0012d 100644
    --- a/kernel/trace/blktrace.c
    +++ b/kernel/trace/blktrace.c
    @@ -15,6 +15,9 @@
    * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
    *
    */
    +
    +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    +
    #include <linux/kernel.h>
    #include <linux/blkdev.h>
    #include <linux/blktrace_api.h>
    @@ -481,6 +484,16 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
    */
    strreplace(buts->name, '/', '_');

    + /*
    + * bdev can be NULL, as with scsi-generic, this is a helpful as
    + * we can be.
    + */
    + if (q->blk_trace) {
    + pr_warn("Concurrent blktraces are not allowed on %s\n",
    + buts->name);
    + return -EBUSY;
    + }
    +
    bt = kzalloc(sizeof(*bt), GFP_KERNEL);
    if (!bt)
    return -ENOMEM;
    --
    2.25.1
    \
     
     \ /
      Last update: 2020-06-29 23:16    [W:4.121 / U:0.280 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site